The present invention relates to a safety air bag or cushion which serves to protect a rider or riders in a automotive vehicle from unexpected danger of injury or death at the time of collision of the vehicle. More particularly, the invention is concerned with an inflating device for such safety air bag adapted to be installed in a small-sized automotive vehicle.
In view of the possible injury to, or danger of erroneous steering operation by, the vehicle rider due to its abrupt or sudden expansion or inflation, the safety air bag should be of such a type that it will not be actuated for inflation at a collision speed of the automobile vehicle below that which is likely to result in injury to the rider if no air bag is provided.
At the present level of technology, the inflating device for the safety air bag is so constructed that it may be actuated to expand the safety air bag when slowing-down in the vehicle running speed to approximately 25 km/h or so will take place in a time instant of approximately 150 m.sec. or shorter. (This reduction in the vehicle running speed will hereinafter be called "speed reduction value V.sub.RS ".) The reason for this setting of the speed reduction value V.sub.RS is due to the fact that the capability of the energy-absorbing type front window glass, steering handle, gauge panel, and various other equipments in the automotive vehicle to protect the vehicle riders from unexpected injury or death at the time of collision of the vehicle is limited to this extent of the speed reduction at the present level of the technology.
In large-sized vehicles, such safety system has already been put into practice by installing in the vehicle cabin a detection device to detect an abrupt reduction in its running speed so that, when the detected value has reached the abovementioned speed reduction value V.sub.RS, an instruction may be given to the safety air bag expanding mechanism to inflate or balloon the same. However, since the small-sized vehicle has no spacious front cabin compartment for the vehicle occupant, if an instruction signal is sent to the inflating device for the safety air bag to be actuated only after the speed change in the vehicle has reached a value corresponding to the speed reduction value V.sub.RS, the vehicle rider will meet with the safety air bag before it is completely inflated, and such premature inflation cannot at all exhibit satisfactory life saving capability.
As the measures for such premature inflation of the safety air bag, if a seismometric weight type sensor is provided at the front end part of the vehicle, an actuating signal for the air bag inflation can be emitted almost simultaneously with the collision. However, this sensing device is so sensitive that it can easily detect a very slight shock of collision and emit a signal when an object of even a small mass collides against the vehicle at a high speed with the result that the safety air bag is disadvantageously actuated when it is not required to be inflated.
In other words, this front sensor tends to operate erroneously, while the cabin sensor brings about delay in the operation, when installed in the small-sized car. As the consequence, it is not possible to solve the abovementioned various points of problem even by arranging these two sensors, i.e., front and cabin, either in series or in parallel.